Growth hormone gene variability and its effects on milk traits in primiparous Sarda goats Maria Luisa Dettori*, Angela Maria Rocchigiani, Sebastiano Luridiana, Maria Consuelo Mura, Vincenzo Carcangiu, Michele Pazzola and Giuseppe Massimo Vacca Dipartimento di Medicina Veterinaria, Università degli Studi di Sassari, via Vienna 2, 07100 Sassari, Italy Received 26 June 2012; accepted for publication 05 December 2012; first published online 23 April 2013 The aim of this research was to investigate variability in each of the five exons of the caprine growth hormone (gGH) gene, in order to establish the possible relationships with milk traits in Sarda breed goat. The general linear model procedure was used to analyse the effects of the single strand conformation (SSCP) profiles on milk traits of 100 lactating goats. Analysis of conformational polymorphism at exons 1–5 revealed a total of 25 differing banding patterns. Sequencing revealed 21 nucleotide changes (compared with GenBank D00476): 14 were polymorphic and 7 monomorphic; 19 in exonic regions, 5 of which were nonsynonymous. A SNP upstream of the transcription initiation codon (c.-3A > G) and an indel (c.*29_30insC) in the 3′UTR, were detected. Alignment of 4 cloned sequences including the entire gGH gene led to the identification of 22 nucleotide variations within the intron regions, including two indels. Association analysis revealed that each exon, except exon-1, affected milk yield, exons 1 and 3 influenced milk fat percentage, and all exons, except exon-2, had an effect on protein percentage, supporting previous results in livestock. The variability detected at the caprine GH gene might provide useful information for the phylogeny of ruminants and, more importantly, have implications on the biological function of the growth hormone and on those traits resulting from its physiological action, including milk production and composition. The caprine GH gene may become a useful molecular marker for a more effective genetic selection for milk production traits in goats. Keywords: Goat, growth hormone, gGH gene, genotype, polymorphism. The growth hormone (GH) is synthesised and secreted by the anterior pituitary somatotroph cells and its secretion is tightly regulated, stimulated by growth hormone–releasing hor- mone (GHRH) and inhibited by somatostatin (SS or GHIH, growth hormone-inhibiting hormone), both secreted by the hypothalamus. The GH is released into systemic circulation and causes the secretion of the insulin like growth factor – 1 (IGF-1) in target tissues, it also causes a series of direct metabolic effects as it is both hyperglycaemic and lipolytic (Polkowska et al. 2011). As a consequence, the growth hormone is directly involved in animal processes such as metabolism (Barrera-Saldaña et al. 2010), growth (Hua et al. 2009), reproduction (Scaramuzzi et al. 1999) and lactation (Baldi, 1999). The GH gene spans 2·6 to 3·0 kbp in most mammalians and comprises five exons. In cattle, the growth hormone is synthesised by a single gene, the bGH (bovine GH) gene, mapped to chromosome 19 (19q22) (Fries, 1993). A close relationship between genetic polymorphisms at the bGH gene and milk fat (Falaki et al. 1996) and milk protein percentage (Lagziel et al. 1999) has been reported in this species. In addition, a nucleotide (nt) variation located on the third intron of bGH gene has been associated with milk yield (Zhou et al. 2005). The ovine GH (oGH) gene has been mapped to chromosome 11 (11q25) (Ofir & Gootwine, 1997); significant associations between oGH genotypes and milk yield have been evidenced in Serra da Estrela, a Portuguese breed of sheep (Marques et al. 2006). The caprine GH (gGH) gene, syntenic to bovine, has been mapped on 19q22. The caprine GH is a copy number variant (CNV), showing two different alleles: the Gh1 allele has a single copy of the gene (named GH1), while the Gh2 allele is duplicated and contains the GH2 and GH3 copies (Wallis et al. 1998). Investigations on gGH gene genetic variability have highlighted significant correlations with: milk yield and protein percentage in the Portuguese Algarvia (Malveiro et al. 2001) and Serrana breeds (Marques et al. 2003); body weights in the Indian Sirohi *For correspondence; e-mail: mldettori@uniss.it Journal of Dairy Research (2013) 80 255–262. © Proprietors of Journal of Dairy Research 2013 doi:10.1017/S0022029913000174 255